# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: YetiWoodz on 16/12/2019 18:47:15

Title: What happens to the direction of wind that hits a flat bladed wind turbine?
Post by: YetiWoodz on 16/12/2019 18:47:15
Does the wind move in a circle like in the picture? Does it move downward? Does it move backwards? Does it keep going straight?
Title: Re: What happens to the direction of wind that hits a flat bladed wind turbine?
Post by: YetiWoodz on 16/12/2019 19:05:27
Btw, the face of the blades are facing the wind if it even matters.
Title: Re: What happens to the direction of wind that hits a flat bladed wind turbine?
Post by: Bill S on 17/12/2019 20:24:28
Just a guess.  Consider the lowest blade.  The wind hits the blade, which moves to the left.  The wind is deflected to the right (=/opp force).  Because the blade is attached to a spindle, the fan rotates.  The wind continues in a L to R, but turbulence introduced by following blades will be a complicating factor.

Watch this space for a real answer. :)
Title: Re: What happens to the direction of wind that hits a flat bladed wind turbine?
Post by: alancalverd on 17/12/2019 23:33:12
All the air coming from the left has to end up on the right. Placing a flat paddle in the way just induces turbulence in the flow.

A symmetric array of flat blades won't turn. The force on the upper blades is exactly the same as that on the lower blades. But if you curve (aerofoil) or twist (child's toy windmill) or feather the blades, the force is unbalanced and the assembly can spin. This produces less turbulence downstream and you can extract useful energy from the rotor.
Title: Re: What happens to the direction of wind that hits a flat bladed wind turbine?
Post by: Bill S on 18/12/2019 12:11:12
I assumed from the illustration that although the blades were flat (not curved), they must have been angled.
Title: Re: What happens to the direction of wind that hits a flat bladed wind turbine?
Post by: evan_au on 18/12/2019 21:22:24
The wind downstream of a windmill is a rotating vortex, so a single windmill can't extract all the energy from the wind.

In theory, if you have two propellers rotating in opposite directions, you can extract more energy from the wind.

The Russians have used this principle in some large propeller-driven planes, with contra-rotating propellers.

However, the blades coming close together leads to considerable noise - something undesirable in a "peaceful" windfarm.

But I don't see why every second windmill in a windfarm couldn't rotate in opposite directions. That would reduce the "shielding" effect that windmills have on downwind windmills, without increasing the noise...
See: https://en.wikipedia.org/wiki/Contra-rotating_propellers
Title: Re: What happens to the direction of wind that hits a flat bladed wind turbine?
Post by: Bill S on 19/12/2019 02:33:03
The Fairly Gannet had counter-rotating props, if I remember correctly.
Title: Re: What happens to the direction of wind that hits a flat bladed wind turbine?
Post by: Petrochemicals on 20/12/2019 11:31:58
It hits the blade and continues, it is turbulent and is smoothed again gy the air that is not passing through the turbines. This also means that the air that did not pass the turbines is slowed, being warm moist air, this causes it to dump its water content from a low atmospheric level warming and wetting the area keeping energy close to the surface, thus we have our warm moist conditions.